The present invention relates to a canned motor pump having no shaft seal part.
A canned motor pump which is a kind of leakless pumps of a prior art has, unlike pumps in general use, no shaft seal part for restricting liquid leakage at a shaft area of a pump casing in which the pump shaft is mounted through. For example, as shown in FIG. 3, the canned motor pump comprises a pump casing 40, a frame 41 connected to the pump casing 40, a stator 42 housed in the frame 41, a stator can 43 hermetically enclosing the stator 42 in a canned condition, a rotor can 44 hermetically enclosing a rotor, bearings 46 and 47 supporting a shaft 45 of the rotor, an impeller 48 secured on one end of the shaft 45, and a circulating pipe 51.
The circulating pipe 51 is provided for leading a part of a liquid to be discharged from a casing flange 49 part into the inside of the motor, or the inside of the stator can 43. In this type of canned motor pump, a part of the liquid being handled is circulated as a circulating liquid in the motor, for the purposes of lubricating and cooling the bearings 46 and 47, and of cooling the motor coil with heat generation.
In case of a canned motor pump of such a constitution, the liquid handled will not leak out, and therefore the canned motor pump is suitable for handling a deleterious liquid for the human body, an explosive or inflammable liquid, and corrosive liquid. Also, since no outside air is drawn in, the canned motor pump is suitable for operation in a vacuum system and for use in handling a liquid which is likely to deteriorate it's quality when exposed to the outside air. This type of pump, therefore, has wide applications in the chemical, nuclear power, and energy industries.
This known canned motor pump, however, when a liquid liable to polymerization, for example an acrylic monomer, a liquid including a polymer, or a liquid including an adherent substance is handled, there takes place, during operation, a polymerization reaction or the increase of the viscosity in a circulating liquid owing to a frictional heat occurring at the pump shaft bearing part and/or heat produced at the motor coils. In consequence, there arises such a problem that the circulating liquid for cooling the motor falls to circulate normally. Provided that the liquid fails in normal circulation as described above, it becomes necessary to stop pump operation once to provide a cooling period. Once the pump is stopped, the whole system will be greatly affected. To cope with this problem, therefore, there has been demanded a canned motor pump which is capable of controlling heat generation stated above.